Stabilization of photographic silver halide emulsions



Nov. 6,1962 F. D. ALLEN ETAL STABILIZATION OF PHOTOGRAPHIC SILVER HALIDE EMULSIONS Filed July 17, 1959 lhur HJIerz Normanw INVENTORS' .AITORNEYS Fr ankD. Allen Ar 3,062,654 STABILIZATION UF PHOTQGRAPHHC SILVER HALIDE EMULSHONE;

Frank D. Allen, Arthur H. Herz, and Norman W. Kalenda, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed July 17, 1959, Ser. No. 827,309 9 Claims. (Cl. 96-103) This invention relates to the stabilization of photographic silver halide emulsions, and more particularly, to a method of inhibiting development of spontaneous fog without adversely affecting the sensitivity of the photographic silver halide emulsions.

It is well known that photographic emulsions on storage tend to lose sensitivity and to become spontaneously developable without exposure to light. There is normal- 1y a detectable amount of the silver salt reduced during development in the areas where no exposure was given; this is commonly called fog, and sometimes called chemical fog where it is necessary to distinguish between it and the eiiects of accidental exposure to radiation; in this invention, We are not concerned with the latter.

Fog depends both on the emulsion and the conditions of development; for a given emulsion it increases with the degree of development. With constant development conditions, it tends to increase with time, temperature and relative humidity of storage conditions; it is common practice to make accelerated tests of the stability of photographic emulsions by storage at increased temperature or humidity, or both. It is, of course, desirable to have emulsions as stable as possible under the conditions of high temperature and humidity which may occur in tropical climates, for example. Fog usually appears over the whole area of the sensitive coating, but when severe, it frequently is non-uniform. Fog may also be caused by exposure to chemicals, for example, hydrogen sulfide and other reactive sulfur compounds, hydrogen peroxide vapor, and strongly reducing materials. While antifoggants and stabilizers may protect, to some extent, against such effects, it is normally understood that an antifoggant protects against spontaneous growth of fog during prolonged storage or storage at high temperatures and humidities, or during development to maximum contrast and speed, or both.

In emulsion technology, the use of certain organic disulfides as chemical sensitizers and stabilizers against incubation fog has been previously described. Unfortunately, many of these disulfides have properties which place them in more than one of the above categories. For example, cystine is known to exhibit both sensitizing and antifoggant behaviour. In like manner, the disulfides obtained from certain mercapto carboxylic acids, such as those described in Matthies et al., U.S. Patent 1,742,042, issued December 31, 1929, have primarily a sensitizing effect on photographic silver halide emulsions, with a much less marked effect upon the stability of the emulsions.

Because of the above facts, the use of such organic disulfides as antifoggants offers practical disadvantages.

Such disulfides having both sensitizing and some stabilizing activity cannot be employed in unsensitized or undersensitized emulsions. In fully sensitized, high-speed emulsions, the sensitizing or desensitizing disulfides, if they are to act as fog restrainers, must be used at narrow and controlled concentration levels, thus making their introduction into the emulsion, for example, by bathing, impractical.

-It is, therefore, an a method of stabilizing object of our invention to provide photographic silver halide emulice sions. Another object is to provide a method of stabilizingphotographic silver halide emulsions without affecting to any material extent the sensitivity of the emulsion. Another object is to provide a method of stabilizing both unsensitized and sensitized emulsions, without introducing any substantial sensitizing or desensitizing effects. Other objects will become apparent from a consideration of the following description and examples.

According to our invention, photographic silver halide emulsions can be stabilized against the formation of spontaneous fog by incorporating therein a dicarboxyalkyldisulfide or a Water-soluble salt of said dicarboxya'lkyldisulfide, provided said dicarboxyalkyldisulfide has a molecular weight of at least 238. v

The dicarboxyalkyldisulfides and their water-soluble salts useful in practicing our invention include those compounds represented by the following general formula:

wherein R and R each represents a methylene group, which may or may not be substituted by hydrocarbon radicals, such as methyl, ethyl, etc., R R R and R each represents a hydrogen atom, a lower alkyl group (e.g., methyl, ethyl, etc.), or an aralkyl group (e.g., benzyl, fl-phenylethyl, etc.), M and M each represents a cation such as hydrogen, an alkali metal (e.g., sodium, potassium, etc.), ammonium, substituted (e.g., organic) ammonium (e.g., pyridinium, triethanolammonium, etc.), and m and it each represents an integer of from O to about 8, provided that said compounds contain at least 8 carbon atoms. Typical compounds useful in practicing our invention include the following:

I CH3 CH3 5,5-dimethyl-5,5-dithi0divaleric acid For the purpose of inhibiting fog formation, the disulfides of our invention can be added to the emulsion during the process of manufacture in order to avoid loss of sensitivity and to inhibit the growth of fog with passage of time under non-ideal conditions of storage.

An aqueous solution of the disulfides of our invention when added at suitable concentration to unsensitized, chemically sensitized, or optically sensitized photographic emulsions does not appreciably affect the sensitometric values for sensitivity and fog when measurements are made soon after coating. When sensitometric measurements are made at appreciable intervals of time, at elevated temperatures and dry or somewhat humid conditions, the disulfides of our invention do stabilize speed and maintain fog at a low level.

The preparation of silver halide emulsions involves three separate operations: (1) the emulsification and digestion or ripening of the silver halide, (2) the freeing of the emulsion from excess soluble salts, usually by washing, and (3) the second digestion or after-ripening to obtain increased sensitivity. (Mees, The Theory of the Photographic Process (1942)). We prefer to add the fog-inhibiting agents after the final digestion or afterripening, although they can advantageously be added prior to digestion.

If desired, the disulfides of our invention can be incorporated in the emulsions without adverse efiects by bathing techniques known to those skilled in the art.

The photographic emulsions used in practicing our invention are of the developing-out type.

The emulsions can be chemically sensitized by any of the accepted procedures. The emulsions can be digested with naturally active gelatin, or sulfur compounds can be added such as those described in Sheppard U.S. Patent 1,574,944, issued March 2, 1926, Sheppard et al. U.S. Patent 1,623,499, issued April 5, 1927 and Sheppard et al., U.S. Patent 2,410,689, issued November 5, 1946.

The emulsions can also be treated with salts of the noble metals such as ruthenium, rhodium, palladium, iridium, and platinum. Representative compounds are ammonium chloropalladate, potassium chloroplatinate, and sodium chloropalladite, which are used for sensitizing in amounts below that which produces any substantial fog inhibition, as described in Smith and Trivelli U.S. Patent 2,448,060, issued August 31, 1948.

The emulsions can also be chemically sensitized with gold salts as described in Waller et al. U.S. Patent 2,399,- 083, issued April 23, 1946, or stabilized with gold salts as described in Damschroder U.S. Patent 2,597,856, issued May 27, 1952, and Yutzy and Leermakers U.S. Patent 2,597,915, issued May 27, 1952. Suitable compounds are potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and Z-aurosulfobenzothiazole methochloride.

The emulsions can also be chemically sensitized with reducing agents such as stannous salts (Carroll U.S. Patent 2,487,850, issued November 15, 1949), polyamines, such as diethyl triamine (Lowe and Jones U.S. Patent 2,518,- 698, issued August 15, 1950), polyamines, such as spermine (Lowe and Allen U.S. Patent 2,521,925, issued September 12, 1950), or bis(,B-aminoethyl)sulfide and its water-soluble salts (Lowe and Jones U.S. Patent 2,521,- 926, issued September 12, 1950).

The emulsions can also be optically sensitized with cyanine and merocyanine dyes, such as those described in Brooker U.S. Patents 1,846,301, issued February 23, 1932; 1,846,302, issued February 23, 1932; and 1,942,854, issued January 9, 1934; White U.S. Patent 1,990,507, issued February 12, 1935; Brooker and White U.S. Patents 2,112,140, issued March 22, 1938; 2,165,338, issued July 11, 1939; 2,493,747, issued January 10, 1950 and 2,739,- 964, issued March 27, 1956; Brooker and Keyes U.S. Patent 2,493,748, issued January 10, 1950; Sprague U.S. Patents 2,503,776, issued April 11, 1950, and 2,519,001, issued August 15, 1950; Heseltine and Brooker U.S. Patent 2,666,761, issued January 19, 1954; Heseltine U.S. Patent 2,734,900, issued February 14, 1956; VanLare U.S. Patent 2,739,149, issued March 20, 1956; and Kodak Limited British Patent 450,958, accepted July 15, 1936.

The emulsions may also contain speed-increasing compounds of the quaternary ammonium type of Carroll U.S. Patent 2,271,623, issued February 3, 1942; Carroll and Allen U.S. Patent 2,288,226, issued June 30, 1942; and Carroll and Spence U.S. Patent 2,334,864, issued November 23, 1943; and the polyethylene glycol type of Carroll and Beach U.S. Patent 2,708,162, issued May 10, 1955, and the thioether compounds of Graham and Sagal U.S. application Serial No. 779,839, filed December 12, 1958 (now U.S. Patent 3,046,129, issued July 24, 1962) and the Dann and Gates U.S. application Serial No. 797,577, filed March 6, 1959.

The emulsions may contain a suitable gelatin plasticizer such as glycerin; a dihydroxy alkane such as 1,5-pentane diol as described in Milton and Murry U.S. application Serial No. 588,951, filed June 4, 1956 (now U.S. Patent 2,960,404, issued November 15, 1960); an ester of an ethylene bis-glycolic acid such as ethylene bis(methyl glycolate) as described in Milton U.S. application Serial No. 662,564, filed May 31, 1957 (now U.S. Patent 2,904,434, issued September 15, 1959); bis-(ethoxy diethylene glycol) succinate as described in Gray U.S. application Serial No. 604,333, filed August 16, 1956 (now U.S. Patent 2,940,854, issued June 14, 1960), or a polymeric hydrosol as results from the emulsion polymerization of a mixture of an amide of an acid of the acrylic acid series, an acrylic acid ester and a styrene-type compound as described in Tong U.S. Patent 2,852,386, issued September 16, 1958. The plasticizer may be added to the emulsion before or after the addition of a sensitizing dye, if used.

The emulsions may be hardened with any suitable hardener for gelatin such as formaldehyde; a halogensubstituted aliphatic acid such as mucobromic acid as described in White U.S. Patent 2,080,019, issued May 11, 1937; a compound having a plurality of acid anhydride groups such as 7,8-diphenylbicyclo (2,2,2)-7-octene-2,3,5, 6-tetracarboxylic dianhydride, or a dicarboxylic or a disulfonic acid chloride such as terephthaloyl chloride or naphthalene-1,S-disulfonyl chloride as described in Allen and Carroll US. Patents 2,725,294, and 2,725,295, both issued November 29, 1955; a cyclic 1,2-diketone such as cyclopentane-1,2-dione as described in Allen and Byers U.S. Patent 2,725,305, issued November 29, 1955; a bisester or" methane-sulfonic acid such as 1,2-di-(methane-sulfonoxy)-ethane as described in Allen and Laakso U.S. Patent 2,726,162, issued December 6, 1955; 1,3-dihydroxymethylbenzimidazol-Z-one as described in July, Knott and Pollak US. Patent 2,732,316, issued January 24, 1956; a dialdehyde or a sodium bisulfite derivative thereof, the aldehyde groups of which are separated by 3 carbon atoms, such as fi-methyl glutaraldehyde bissodium bisulfite as described in Allen and Burness U.S. patent application Serial No. 556,031, filed December 29, 1955 (now abandoned); a bis-aziridine carboxamide such as trimethylene bis(1-aziridine carboxamide) as described in Allen and Webster U.S. patent application Serial No. 599,891, filed July 25, 1956 (now U.S. Patent 2,950,197, issued August 23, 1960); or 2,3-dihydroxy dioxane as described in Jefireys U.S. Patent 2,870,013, issued January 20, 1959.

The emulsions may contain a coating aid such as saponin; a lauryl or oleyl monoether of polyethylene glycol as described in Knox and Davis U.S. Patent 2,831,- 766, issued April 22, 1958; a salt of a sulfated and alkylated polyethylene glycol ether as described in Knox and Davis U.S. Patent 2,719,087, issued September 27, 1955; an acylated alkyl taurine such as the sodium salt of N-oleoyl-N-methyl taurine as described in Knox, Twardokus and Davis U.S. Patent 2,739,891, issued March 27, 1956; the reaction product of a dianhydride of tetracarboxybutane with an alcohol or an aliphatic amine containing from 8 to 18 carbon atoms which is treated with a base, for example, the sodium salt of the monoester of tetra-carboxybutane as described in Knox, Stenberg and Wilson U.S. Patent 2,843,487, issued July 15, 1958; a water-soluble maleopimarate or a mixture of a water-soluble maleopimarate and a substituted glutamate salt as described in Knox and Fowler U.S. Patent 2,823,123, issued February 11, 1958; an alkali metal salt of a substituted amino acid such as disodium N-(carbo-p-tert. octylphenoxypentaethoxy)glutamate as described in Knox and Wilson U.S. patent application Serial No. 600,679, filed July 30, 1956 (now U.S. Patent 3,038,804, issued June 12, 1962); or a sulfosuccinamate such as tetrasodium N-(1,2-dicarboxyethyl)-N-octadecyl sulfosuccinamate or N-lauryl disodium sulfosuccinamate as described in Knox and Stenberg U.S. patent application Serial No. 691,125, filed October 21, 1957 (now U.S. Patent 2,992,108, issued July 11, 1962).

The addenda which we have described may be used in various kinds of photographic emulsions. In addition to being useful in X-ray and other nonoptically sensitized emulsions they may also be used in orthochromatic, panchromatic, and infrared sensitive emulsions. They may be added to the emulsion before or after any sensitizinzg dyes which are used. Various silver salts may be used as the sensitive salt such as silver bromide, silver iodide, silver chloride, or mixed silver halides such as silver chlorobromide or silver bromoiodide. The agents may be used in emulsions intended for color photography, for example, emulsions containing color-forming couplers or emulsions to be developed by solutions containing couplers or other color-generating materials, emulsions of the mixed-packet type, such as described in Godowsky US; Patent 2,698,794, issued January 4, 1955; or emulsions of the mixed-grain type, such as described in Carroll and Hanson U.S. Patent 2,592,243, issued April 8, 1952. These agents can also be used in emulsions which form latent images predominantly on the surface of the silver halide crystal or in emulsions which form latent images predominantly inside the silver halide crystal, such as those described in Davey and Knott U.S. Patent 2,592,250, issued April 8, 1952.

These may also be used in emulsions intended for use in diffusion transfer processes which utilize the undeveloped silver halide in the nonimage areas of the negative to form a positive by dissolving the undeveloped silver halide and precipitating it on a receiving layer in close proximity to the original silver halide emulsion layer. Such processes are described in Rott U.S. Patent 2,352,- 014, issued June 20, 1944, and Land U.S. Patents 2,584,- 029, issued January 29, 1952; 2,698,236, issued December 28, 1954, and 2,543,181, issued February 27, 1951; and Yackel et al. U.S. Patent application Serial No. 586,705, filed May 23, 1956 (now U.S. Patent 3,020,155, issued February 6, 1962). They may also be used in color transfer processes which utilize the diffusion transfer of an image-wise distribution of developer, coupler or dye, from a light-sensitive layer to a second layer, while the two layers are in close proximity to one another. Color processes of this type are described in Land U.S. Patents 2,559,643, issued July 10, 1951, and 2,698,798, issued January 4, 1955; Land and Rogers Belgian Patents 554,933 and 554,934, granted August 12, 1957; Internation Polaroid Belgian Patents 554,212, granted July 16, 1957, and 554,935, granted August 12, 1957; Yutzy U.S. 'Patent 2,756,142, granted July 24, 1956, and Whitmore and Mader U.S. patent application Serial No. 734,141, filed May 9, 1958.

In the preparation of the silver halide dispersions employed for preparing silver halide emulsions, there may be employed as the dispersing agent for the silver halide in its preparation, gelatin or some other colloidal material such as colloidal albumin, a cellulose derivative, or a synthetic resin, for instance, a polyvinyl compound. Some colloids which may be used are polyvinyl alcohol or a hydrolyzed polyvinyl acetate as described in Lowe U.S. Patent 2,286,215, issued June 16, 1942; a far hydrolyzed cellulose ester such as cellulose acetate hydrolyzed to an acetyl content of 1926% as described in U.S. Patent 2,327,808 of Lowe and Clark, issued August 24, 1893; a water-soluble ethanolamine cellulose acetate as described in Yutzy U.S. Patent 2,322,085, issued June 15, 1943; 2. polyacrylamide having a combined acrylamide content of 30-60% and a specific viscosity of 025-15 on an imidized polyacrylamide of like acrylamide content and viscosity as described in Lowe, Minsk and Kenyon U.S. Patent 2,541,474, issued February 13, 1951; zein as described in Lowe U.S. Patent 2,563,791, issued August 7, 1951; a vinyl alcohol polymer containing urethane carboxylic acid groups of the type described in Unruh and Smith U.S. Patent 2,768,154, issued October 23, 1956; or containing cyano-acetyl groups such as the vinyl alcohol-vinyl cyanoacetate copolymer as described in Unruh, Smith and Priest '6 U.S. Patent 2,808,331, issued October 1, 1957; or a polymeric material which results from polymerizing a protein or a saturated acylated protein with a monomer having a vinyl group as described in U.S. Patent 2,852,382, of 11- lingsworth, Dann and Gates, issued September 16, 1958.

If desired, compatible mixtures of two or more of these colloids may be employed for dispersing the silver halide in its preparation. Combinations of these sensitizers, hardeners, etc., may be used.

The disulfides useful in practicing our invention can be added to the photographic emulsions prior to the final digestion, if desired. Generally, these compounds can be added from substantially neutral aqueous solution so that the pH of the emulsion is not disturbed. In the case of compounds containing free carboxylic acid groups, this means that these carboxylic acid groups will be at least partially neutralized. In any event, it can be seen that the disulfides of our invention exist in the emulsion in ionic form, inasmuch as they are used in small quantities, and the emulsions useful in practicing our invention ordinarily contain substantial amounts of water. However, the disulfides useful in practicing our invention can be added to the emulsions in the form of free acids, particularly where the addition is made to an acidic type emulsion.

The amount of disulfide compound added to the emulsions of our invention can be varied, depending upon the particular emulsion, the silver halide content of the emulsion, etc. In general, we have found that from about 0.1 to 15.0 grams of disulfi-de per mole of silver halide can advantageously be employed in our invention. One of the outstanding advantages of the disulfides of our invention, as compared with the disulfides which have been previously described in the prior art, is that they can be used in quite substantial quantities without introducing serious desensitizing effects. Moreover, as indicated above, the disulfides useful in our invention advantageously have little or no sensitizing action on their own, and hence, they can be used to stabilize emulsions which have already been finished to their optimum or near-optimum speeds. Thus, addition of our compounds to such finished emulsions does not result in any substantial desensitizing effect, such as might ordinarily be expected.

The advantages of the disulfides of our invention over the lower homologs of the prior art is illustrated schematically in the accompanying drawing, which shows that the disulfides of our invention do not have any substantial sensitizing action, whereas the lower homologs of the prior art have a marked sensitizing action. In fact, these lower homologs are ordinarily employed as sensitizers for silver halide emulsions, and they have found little or no use in the stabilization of such emulsions.

The following examples well serve to illustrate the useful stabilizing effect of the dicarboxyalkyldisulfides useful in practicing our invention. A series of coatings was made on ordinary photographic film support, such as cellulose acetate, of an ordinary photographic high-speed bromiodide emulsion to which had been added one of the dicarboxyalkyldisulfides of our invention in the concentration shown in the following table. The compounds were added from substantially neutral aqueous solutions and comparison were made with an identical batch of emulsion which contained no antifoggant compound. After coating each series of emulsions on a cellulose acetate support, they were dried and then exposed on an intensity scale sensitometer (Kodak Type Ib) and developed for about 4 minutes at 68 F. in a developer havingthe following composition:

Water, about F. (50 C.) cc 500 N-rnethyl-p-aminop-henol sulfate grams 2.0 Sodium sulfite, desiccated do 90.0 Hydroquinone do 8.0 Sodium carbonate, monohydrated do 52.5 Potassium bromide do 5.0

Cold water to make 1.0 liter.

c eeses Fresh tests and incubation tests (one week at 120 F., constant relative humidity of about 50%, and in some cases for two weeks under the same conditions) were also run for the same emulsion series with development under the same conditions. The relative speed and fog for each of the series of coatings were then measured, the speed being determined at a point about 0.3 density above fog.

In the following table the compound numbers correspond to the numbers used above for the specific disulfides. The compound numbers A and B represent compounds which have been previously used in the prior art to sensitize photographic silver halide emulsions. These data are included to show that such compounds do not provide the useful stabilizing effect provided by the compounds of our invention. In each coating series, the same emulsion batch was used, although dif ferent emulsion batches were used for some of the coating numbers identified in the table. Wherever a different emulsion batch was used, a control series was run for that batch to show the degree of improvement obtained.

In coating No. 3, the silver bromiodide emulsion was a fast panchromatically sensitized bromiodide emulsion. The same general type of emulsion was used in coating series No. 4. The results of these coating series are given in the following table:

One Week Incubation Test Fresh Test Two Week Incubation Test,

Fog

Coating N0.

Addendum Compound N o. (g/mo]. AgX) A-dithiodiacetic acid.

B3,3-dithiodipropionic acid.

The advantages in using disulfides of Formula I above, as compared with the lower homologs are shown graphically in the accompanying drawing.

In FIGURE I, the curves represent the sensitivity curvs of ordinay photographic silver halide emulsions containing a homologous series of dicarboxyalkyldisulfides. These disulfides (in approximately molar equivalent amounts) were added to aliquot portions of the same batch of coarse-grained silver bromiodide emulsions from substantially neutral aqueous solutions. All of the emulsions were held for about 30 minutes at 60 C. and then coated on ordinary cellulose acetate film. Curve 1 represents the sensitivity of the bromiodide emulsion containing 2.7 grams of dithiodiacetic acid per mole of silver bromiodide. Curve 2 represents the sensitivity of the same emulsion containing 3.15 grams of 3,3- dithiodipropionic acid. Curve 3 represents the sensitivity of the same emulsion containing 3.6 grams of 4,4-dithiodibutyric acid per mole of silver bromiodide. A curve substantially identical to curve 3 was obtained for the untreated emulsion (control) and for the same emulsion containing 4.0 grams of 5,5-dithiodivaleric acid per mole of silver bromiodide. These curves, commonly called H and D curves, shown that the disulfides of the present invention have no substantial sensitizing effect on silver halide emulsions. Yet, the data in the accompanying table show that they have a much more useful stabilizing etfe-ct than the lower homologs used in obtaining curves 1 and 2.

The disulfides useful in stabilizing emulsions according to our invention can be obtained by methods previously described in the prior art. For example, these disulfides can be obtained by the simple oxidation of the corresponding mercaptans, represented by the following general formula:

it. wherein R, R R M and n each have the values given above. Useful oxidizing agents include aqueous solutions of iodine in potassium iodide, hydro-gen peroxide, etc. The following examples will serve to illustrate the preparation of one of the disulfides useful in practicing our invention,

EXAMPLE A q -Mercaptobutyric Acid Equal molar amounts (2 moles) of 'y-butyrolacetone (Cliifs-Dow-Chemical Co.) and thiourea were refluxed 12 hours in the presence of 20 percent excess hydrobromic acid (48 percent). The reaction mixture was made strongly basic with 50 percent sodium hydroxide, refluxed for 3 hours, cooled, and made strongly acidic with concentrated sulfuric acid. The reaction mixture was extracted with ether. The ether extracts were washed with water and dried over anhydrous magnesium sulfate. The ether was removed under vacuum and the product processed by rapid distillation through a 6-inch Vigreux column under reduced pressure.

Yield126 g., 13.1. IOU-110 C. at 5-6 mm. Second cut-29 g., BP. 105 C. at 56 mm.

EXAMPLE B 'y,'y-Dithi0dibutyric Acid 'y-Mercaptobutyric acid (123 g., 1.02 moles) was dissolved in dilute sodium hydroxide. This material was oxidized by the slow addition (dropping funnel) of potassium triiodide solution [potassium iodide (200 g.) dissolved in 800 ml. of water. Iodine (100 g.) is then dissolved in the solution]. After the oxidation was complete, enough dilute (3 percent) sodium thiosulfate solution was added to give a colorless solution. The solution was made strongly acidic with dilute sulfuric acid. The material which separated out was recrystallized from water.

The yield was g. The M.P. was 107109 C.

Compound 3 was synthesized according to the method described by Schoeberl, Berichte 70 (1937), page 1186.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variation and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What we claim is:

1. A photographic silver halide emulsion stabilized with a water-soluble compound selected from the class represented by the following formula:

wherein R and R each represents a methylene group, R R R and R each represents a member selected from the class consisting of a hydrogen atom, a lower alkyl group and an aralkyl group containing from 7 to 8 carbon atoms, M and M each represents a cation, and m and 11 each represents an integer from 0 to 8, provided that said compound contains at least 8 carbon atoms.

silver halide emulsion as defined 2. A photographic substantially unsensiin claim 1, said emulsion being tized.

3. A photographic silver halide emulsion as defined in claim 1, said emulsion being gold sensitized.

4. A photographic silver halide emulsion as defined in claim 1, said emulsion being sulfur sensitized.

5. A photographic silver halide emulsion as defined in claim 1, said emulsion being gold and sulfur sensitized.

6. A photographic silver bromiodide emulsion stabiliZed with a water soluble compound selected from the class represented by the following formula:

wherein R and R each represents a methylene group, R R R and R each represents a member selected from the class consisting of a hydrogen atom, a lower alkyl group and an aralkyl group containing from 7 to 8 carbon atoms, M and M each represents a cation,

10 and m and n each represents an integer from 0 to 8, provided that said compound contains at least 8 carbon atoms.

7. A photographic silver halide emulsion stabilized with a compound selected from the class consisting of (l) 4,4-dithiodibutyric acid and (2) water-soluble salts of 4,4-dithiodibutyric acid.

8. A photographic silver halide emulsion stabilized with a compound selected from the class consisting of (1) 5,5dithiodivaleric acid and (2) a water-soluble salt of 5,5-di-thiodivaleric acid.

9. A photographic silver halide emulsion stabilized with a compound selected from the class consisting of (1) 2,2,2,2-tetramethyl-2,2-dithiodiacetic acid and (2) a Water-soluble salt of 2,2,2,ZQtetramethyl-LZ'-dithiodiacetic acid.

References Cited in the file of this patent UNITED STATES PATENTS 1,742,042 Matthies 'et al. Dec. 31, 1929 

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION STABILIZED WITH A WATER-SOLUBLE COMPOUND SELECTED FROM THE CLASS REPRESENTED BY THE FOLLOWING FORMULA:
 3. A PHOTOGRAPHIC SILVER HALIDE EMULSION AS DEFINED IN CLAIM 1, SAID EMULSION BEING GOLD SENSITIZED. 